1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same. The present invention is suitable for a video camera, a film-based camera, a digital camera, a TV camera, and a surveillance camera.
2. Description of the Related Art
An image pickup optical system that utilizes an image pickup device and is used for an image pickup apparatus, such as a video camera and a digital still camera, has recently demanded for a zoom lens having a high angle of view and a zoom ratio.
In general, it is necessary for a high zoom ratio of the zoom lens to improve the refractive powers of lens units for variable magnification and to increase a movement amount for zooming. However, such a zoom lens causes large aberrational fluctuations in the zooming and it becomes difficult to obtain a high optical performance over the entire zoom range.
In order to obtain a high angle of view, a high zoom ratio, and a high optical performance over the entire zoom range, it is important to properly set a zoom type, refractive power of each lens unit, and a lens configuration in each lens unit.
There is known a four-unit zoom lens that includes, in order from an object side to an image side, a first lens unit of a positive refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, and a fourth lens unit of a positive refractive power. There is also known a rear focus type four-unit zoom lens configured to move the second lens unit for variable magnification, to move the fourth lens unit for correcting image plane changes associated with the variable magnification, and to provide focusing through the fourth lens unit. See Japanese Laid-Open Patent Nos. 3-215810 and 2000-171713.
It is important for these four-unit zoom lenses to properly set a movement amount of the third lens unit associated with zooming relative to the imaging magnification and the zoom ratio of the second lens unit configured to primarily vary the magnification.
It is also important to properly set a movement amount of the second lens unit associated with zooming and a focal length (a reciprocal of the power) of each of the first, second, and third lens units.
It is difficult to obtain a high optical performance over the entire zoom range and to maintain a wide angle of view and a high zoom ratio unless these configurations are properly set.